Analysis of ASTM D790-72 and its application to reinforced plastic structural members

It has been shown that flexural strength varies with test method. Literature searches reveal that flexural bend testing is simple, cost effective and a very popular method of testing for flexural, tensile and shear strengths. However, a myriad of methods of testing are also being employed to determine these strengths. Test results obtained from this investigation will be used to clarify the need for standardization of testing methods.; With the increased interest in composite structural shapes, it is necessary to evaluate the application of ASTM D-790-92 to full-scale test specimens. Pultruded I-beams and boxes were tested in flexural bending and modification of ASTM D-790-92 was made to include structural shapes. A comparison was made of three-point and four-point bending methods and how flexural strength and modulus of pultruded structural shapes change with load span and support span. Glass/polyester, glass/epoxy composites, glass/vinyl ester and carbon/epoxy composites were tested by the flexural bending method. Tested specimens were examined in an attempt to determine the failure mode and to determine if the equations for stress at the outer fiber as given in ASTM D-790-92 are appropriate for a given failure mode. Stress equations in ASTM D-790-92 are for determining stress when the failure mode is tensile or compressive. Modifications were suggested for the standard in the testing of these structural shapes where needed.; Coupons were cut from the composite beams and test in flexural bending to determine the upper limit of flexural strength of the pultruded beams. Iosipescu shear testing was performed on coupons cut from the beams to determine shear modulus for finite element modeling. Finite element analysis was used to model the structural specimens.